Field of the Invention
This invention relates generally to a method of treating tensile cord for a power transmission belt, the treatment, the cord and the resulting belt, more particularly to polyurea-urethane-treated carbon fiber reinforcement, and specifically to a carbon fiber cord impregnated with a moisture-cured polyurea-urethane composition.
Description of the Prior Art
U.S. Pat. No. 5,807,194 to Knutson et al., the contents of which are hereby incorporated herein in its entirety, discloses a synchronous power transmission belt with a belt body of cast urethane belt material, belt teeth formed of the body, a wear-resistant fabric reinforcement disposed along peripheral surfaces of the belt teeth, and a tensile member of helically spiraled cord embedded in the belt body and of a yarn of carbon fiber, wherein there are interstices between the fibers of the cord and belt material penetrates at least a portion of the cord interstices as the belt is cast so that the cord interstices contain a minimum of about 0.21 mg of belt material per mm3 of cord volume. Penetration of polyurethane elastomer into the cord may give excellent physical adhesion. However, urethane in its cured state as a high modulus belt material may make a particular cord material unacceptable when it penetrates the interstices of the cord because the so penetrated cord may have an unacceptably high bending modulus. Also, the penetrating urethane may transfer too high a strain to filaments comprising the cord and thus cause unacceptable filament breakage resulting in cord failure. Cast polyurethane materials are often of such a viscosity that it is hard to sufficiently impregnate the cord. Problems from insufficient impregnation include fraying of cord, poor fatigue life, etc.
U.S. Pat. No. 5,231,159 to Patterson et al., the contents of which are hereby incorporated herein in its entirety, describes cast or RIM polyurethane compositions useful for belts. The polyurethanes are based on the reaction product of an isocyanate-terminated (preferably polyether) prepolymer, an amine- or hydroxyl-terminated polyol, and a polyamine or polyol chain extender.
U.S. Pat. No. 6,964,626 to Wu et al., the contents of which are hereby incorporated herein in its entirety, discloses improved polyurethane/urea elastomers having high temperature stability to about 140-150° C. and low temperature flexibility at about −35-(−40)° C., for use in dynamic applications. These elastomers are useful for application in belts, specifically in automotive timing or synchronous belts, V-belts, multi-V-ribbed or micro-ribbed belts, flat belting and the like. The polyurethane/urea elastomers are prepared by reacting polyisocyanate prepolymers with symmetric primary diamine chain extenders, mixtures of symmetric primary diamine chain extenders and secondary diamine chain extenders, or mixtures of symmetric primary diamine chain extenders and non-oxidative polyols, which are all chosen to eliminate the need for catalysts via standard molding processes, and to improve phase separation. The polyisocyanate prepolymers are reaction products of polyols which are nonoxidative at high temperatures, such as polycarbonate polyols, polyester polyols, or mixtures thereof, with organic polyisocyanates which are either compact, symmetric and aromatic, such as para-phenylene diisocyanate, 1,5-naphthalene diisocyanate, and 2,6-toluene diisocyanate, or are aliphatic and possess trans or trans,trans geometric structure, such as trans-1,4-cyclohexane diisocyanate and trans,trans-4,4′-dicyclohexylmethyl diisocyanate.
Prior efforts to treat cord with a softer material to make a more flexible cord in polyurethane belts have resulted in belts with lower torque resistance, higher heat build up during flexing, poor resistance to delamination, and the like. Adhesive treatments for carbon fiber cord in general have been less than adequate for demanding belt applications, whether for polyurethane or rubber belts. Representative of prior carbon fiber adhesive treatments are U.S. Pat. Nos. 6,695,733 and 6,945,891 to Knutson, which disclose a toothed rubber belt with resorcinol-formaldehyde-latex (“RFL”) treated carbon fiber tensile cord. Also representative of the carbon fiber adhesive art is the epoxy primer and RFL treatment of U.S. Pat. No. 4,044,540 to Toki et al., and the primer and RFL treatment of U.S. Pat. No. 4,978,409 to Fujiwara et al.
U.S. Pat. Appl. Pub. No. 2005-0271874A1 to Sakajiri et al. discloses carbon fiber sizing treatment with unsaturated urethane compound as the principal component. JP 2005-023480A2 to Sakajiri et al. discloses a resin composition including a polyurethane, an epoxy resin and a crosslinking agent for impregnating a carbon fiber bundle.
U.S. Pat. Pub. No. 2009/0098194A1 describes urea-urethane chemistry.
U.S. Pat. No. 3,962,511 discloses polyurethane compositions for encapsulating textile woven fabric for industrial conveyor belts and a method of applying a polyurethane reaction mixture in an organic solvent solution.
Reference is made to co-pending application Ser. No. 11/947,470 filed on Nov. 29, 2007, and Ser. No. 12/044,957 filed on Mar. 8, 2008, the contents of both of which are hereby incorporated herein in their entireties.